<!DOCTYPE htlm>
<html>
<head>
	<title></title>
	<style type="text/css">
		#leftdiv{
			height: 30px
			width: 100px
			background:yellow;
			float:left;
		}
		#rigthdiv{
			height: 80
			width: 100px
			background:lightblue;
			float:right;
		}
	#common{
		height: 500px;
		width: 100%;
		background: pink;
		clear: right;
	}
</style>
</head>
<body>
<div id="leftdiv">我是左边</div>
<div id="rigthdiv">我是右边</div>
<div id="common">
</div>

</body>
</html>